merge sort Archives - C Program Examples

Merge sort is based on the divide conquer strategy. Array is divided in to two halves.if the array length is n, then it is divided into n/2,n/4,n/8…. and each part is sorted independently, then conquered into the sorted array. The efficiency of merge sort is O(n log n). Read more about C Programming Language .

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#include <stdio.h>
#include <stdlib.h>

#define MAX_ARY 10

void merge_sort(int x[], int end, int start);

int main(void) {
 int ary[MAX_ARY];
 int j = 0;

 printf("nnEnter the elements to be sorted: n");
 for(j=0;j<MAX_ARY;j++)
  scanf("%d",&ary[j]);

 /* array before mergesort */
 printf("Before    :");
 for(j = 0; j < MAX_ARY; j++)
  printf(" %d", ary[j]);

 printf("n");

 merge_sort(ary, 0, MAX_ARY - 1);

 /* array after mergesort */
 printf("After Merge Sort :");
 for(j = 0; j < MAX_ARY; j++)
  printf(" %d", ary[j]);

 printf("n");
 getch();
}

/* Method to implement Merge Sort*/
void merge_sort(int x[], int end, int start) {
 int j = 0;
 const int size = start - end + 1;
 int mid  = 0;
 int mrg1 = 0;
 int mrg2 = 0;
 int executing[MAX_ARY];

 if(end == start)
  return;

 mid  = (end + start) / 2;

 merge_sort(x, end, mid);
 merge_sort(x, mid + 1, start);

 for(j = 0; j < size; j++)
  executing[j] = x[end + j];

 mrg1 = 0;
 mrg2 = mid - end + 1;

 for(j = 0; j < size; j++) {
  if(mrg2 <= start - end)
   if(mrg1 <= mid - end)
    if(executing[mrg1] > executing[mrg2])
     x[j + end] = executing[mrg2++];
    else
     x[j + end] = executing[mrg1++];
   else
    x[j + end] = executing[mrg2++];
  else
   x[j + end] = executing[mrg1++];
 }
}

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